Valve control circuits are prevalent in gas-powered appliances, such as water heaters, furnaces and fireplaces. Such gas-powered appliances may use a self-powered control circuit and/or valve system. In one approach, a thermally activated power source is used to provide electrical power to the control circuit and/or system. Such thermally activated power sources typically have limited voltage potential as well as current generating capacity. Thus, gas-powered appliances using such a thermally activated power source typically use millivolt gas valves to control the flow of gas (e.g., natural gas, propane). For example, in a water heater application, a thermally activated power source may be used to power a low-power control circuit that controls a pilot valve and a main burner valve for the water heater. As was just indicated, these valves are typically millivolt valves, which may be operated with voltages in the millivolt range.
A common arrangement in gas-powered appliances is to employ two gas valves, one valve for a pilot light burner and one valve for a main burner. The pilot light acts an ignition source for the main burner when its valve is opened by the control circuit (e.g., when water in a water heater is to be heated or when a furnace begins a heating cycle). Further, the pilot light also provides thermal energy to the thermally activated power source to power the control circuit and operate the valve(s). The pilot valve in such appliances typically operates as what may be termed a standing pilot valve. A standing pilot valve, when the appliance is in service, remains open to provide for a continuous pilot light to produce electrical power (for the control circuit) and to provide an ignition source for the main burner when its valve is opened by the control circuit.
In such applications, the pilot valve may remain open for long periods of time (e.g., months or years) while the appliance in which it is employed is in service. In the event the pilot valve becomes mechanically stuck in an open position, such as due to corrosion or mechanical failure, a safety concern may be presented. For example, if the pilot flame is somehow extinguished (e.g., due to airflow extinguishing the flame or a temporary loss of gas flow) and gas flow continues or is restored, gas vapor would be continuously emitted into the area where the appliance is installed, thus creating an explosion and or fire danger.
Currently, in order to verify the proper mechanical operation of such gas valve, an appliance in which the valve is employed is taken out of service to verify that the valve closes as expected. Such a technique requires interruption of the operation of the appliance; depends on human intervention and, thus, may go unattended, creating the possible safety risks that were previously described. Therefore, other techniques for periodically verifying the proper operation of a gas valve are desirable.